Barium-lead glass having low power factor



Patented Jan. 22, 19 46 UNITED STATES PATENT OFFICE; a

sanwmmmp 223ml. Low rowim; 4 I

William lloustonArmistead, Jr., Corning, N. Y.,

assignor to Corning Glass Works, Corning, N. Y., a corporation of New York No Drawing. Aipplication July 11, 1944,

' Serial No. 544,468

6 Claims.

This invention relates to glass compositions and has for its primary object to provide a new and useful glass having certain special characteristics 1 making it particularly suitable as an insulating medium for use in electrical condensers for radio circuits. A glass having these characteristics would be a welcome substitute for mica which is ordinarily used for this purpose and which is expensive and requires considerable selection to insure suitable uniformity in quality. Glass, on the other hand, can,be manufactured relatively cheaply and with great uniformity in composition and properties. However, no glass has heretofore been devised which combines the desired characteristics to the extent that does the glass herein claimed.

The desired characteristics are:

A power factor less than 07%, as measured at a frequency of one megacycle at room temperature.

A dielectric constant of at least 4 and preferably '7 or 8.

A temperature coeflicient less than 100 parts per million per'degree centigrade. By tempera- .ture coefllcient is meant the rate of A change of dielectric constant with change of temperature.

miscible phases or compositions on cooling and are so weak structurally thatthey crumble.

I have found that the addition of to 15% of alumina to such compositions prevents the formation of separate phases and renders all components miscible. At the same time the chemical stability of the glasses is improved, the power factor is decreased, the dielectric constant is increased, and-the temperature coefllcient is not substantially changed. This result is entire- 1y unexpected, because the introduction of alumina into an alkali containing borosilicate raises the power factor by as much as .02% for every 1% of alumina. The presence of alumina is so effective in maintaining a lower power factor, a high dielectric constant and low temperature coeflicient that the silica content can be reduced to a low value or even omitted without losing the benefit of my invention.

In general, my new glasses consist of a homogeneous mixture of 0% to 50% S:- 5% to 'AlzOs, 10% to 75% B203, and 10% to P100 plus BaO, the ratio PbO/BaO being at least 3 when the total amount of these oxides is high.

This is an important requirement since it is desirable'that the capacity of a condenser should 1 not change appreciably over the temperature range in which it is-to be used. Most glasses do not meet this requirement. 1

A softening temperature not greater than 800 0., being that temperature at which a thread of glass one millimeter in diameter and twentythree centimeters long will elongate at the rate of one millimeter per minute when heated throughout the upper nine centimeters of its length.

Any and all of obtained at the sacrifice of others. Many glasses are known which have low power factors but they lack one or more of the above mentioned properties and hence have not been entirely suitable for use in the insulation of condensers for circuits carrying radio frequency currents. In such circuits the power losses caused by lack of these properties may be quite substantial. The prob-.-

lem solved by me has been to obtain all of the desired properties in one glass.

Pure silica has a very low power factor and also a sufficiently low temperature coeflicient for the present purpose but the high fusing point of these properties may easily be 60 50 30 30...--- ill l0 l0 10 10 5 10 30- 2o 30 30 2o 5 10 20K 1o 10..... 5 10. 10 2o 15 2 :0 0 Poweriactonpercent .070 .067 .045 .060 .067 .064 .058 .065 Dielectncconstant--..- 7.13 7.35 4.5 5.5 6.1 6.2 5.1 7.1 Temp. coeil. ppm. per r 0.. so to 64 70 so so so Soiteningiemp. "C 650 688 790 796 667 645 525 642 Expansion coell. X10". 50.9 50 37 39 49.5 47.8 67 51 factors can be lowered somewhat further by the introduction of fluorine, preferablyby the addition of 5% to 10% of'lead fluoride and/or barium fluoridein lieu of the corresponding oxide or oxides.

As examples of glasses in accordance with my invention, the following compositions, calculated in percent by weight from their respective batches together with their properties are given:

The values for power factor were measuredby the method known as ASTM D--42T, set forth on page 1148 et seq., part III of the ASTM standards for 1942. Comparison of glasses 1 and 2 shows that power factor decreases and dielectric constant increases with increase 'in alumina. Composition 8 contains barium fluoride and shows a slight decrease in power factor and softening point over composition 1 which containsno fluorine but is otherwise similar to composition 8.

Similar compositions containing PbO butno E10 and containing BaO but no'PbO are described, and claimed in applications Serial Numbers 544,466 and 544,467, respectively, filed by me on this date and assigned to the assignee of this application.

I claim:

per degree-C., a softening point less than 800 0., and consisting of compounds of'lead, barium, aluminum, boron and silicon in proportions equivalent to to 50% $102, to 15% A120:.

1. A glass havinga power factor less than 07%, Y

' 'a dielectric constant greater than 4, a temperature coeflicient less than 100 parts per million per degree C., a softening point less than 800 C.,

and consisting of compounds of lead, barium,

aluminum, boron and silicon in proportions equivalent to 0% to 50% S102, 5% to 15% A1203,

10% to 75% B003, and 10% t0 40% (PbO-i-BaO) the ratio PhO/BaO being at least 3 when the total PhD and B90 is near 40%.

2. A glass having a power factor less than..07% a dielectric constant greater than 4, a temperature coeflicient less than 100 parts per million per degree C., a softening point less than 800? C., and consisting of 0% to 50% S102, 5% to 15% A1903, 10% to 75% B203, and 10% to 40% (PbO+BaO), the ratio'PbO/BaO being at least -3 .when the-total PhD and mo is near 40%.

3. A glass having a power factor less than 07%,

a dielectric constant greaterthan 4, a temperature coefllcient less than 100 parts per million per degree C., a softening point less than 800 C.,

10% to 75% 1310;, and 10% to (PbO-i-BaO), and a small amount of fluorine, the ratio PbO/BaQ being at least 3 when the total PbO and BaO is near 40%.

4. A glass having a power factor less than 07%, a dielectric constant greater than 4, a temperature coe'flicient less than 100 parts per million per degree 0., a softening point less-than 800 C., and consisting of 0% to SiO:, 5% to 15% A1203, 10% to 1320:, and 10% to 40% (Pb0+Ba0), the ratio PbO/BaO being at least 3 when the total Pb0 plus 13:10 is near 40%, and showing by analysis the presence offluorine.

5. A glass having a power factor less than 07%,

a dielectric constant greater than 4, a temperature coemcient less than parts per million and consisting of compounds of lead, barium, aluminum, boron and silicon in proportions equivalent to approximately 30% SiOz, 10% A1203,

30% Back, 10% B110, and 20% PhD; 

